1. Field of the Invention
The invention relates generally to integrated circuit design, fabrication, and test and more specifically relates to circuits added to an integrated circuit application design to allow dynamic and flexible generation of an interrupt signal from the integrated circuit based on internal states of the integrated circuit not exposed to the external processor coupled to the application circuit.
2. Discussion of Related Art
Application specific integrated circuits perform a number of useful functions in electronic circuit designs. Many application integrated circuits, for example, provide I/O or other interface features for use by an attached general or special purpose processor. Other exemplary application specific integrated circuits provide computational or data manipulation assist logic for particular application needs. In general, all such integrated circuits that are adapted for coupling to an associated general or special purpose processor do so by providing a documented programming interface between the application specific integrated circuit and the attached processor. This programming interface typically defines a set of locations or ports that may be read and/or written by the external processor to interact with the features of the application specific integrated circuit. Often these locations/ports represent a set of registers in which defined fields or bits are used for configuring operation of the application circuit and/or for sensing particular status as regards operation of the application specific integrated circuit.
Although significant functionality of the application circuit may be presented to the processor through the specified, supported, programming interface, in circuit test or debug environments substantial additional information regarding operation of the application specific integrated circuit may be useful. However, such additional internal signals are generally unavailable to the standard processor interface. Rather, the application specific integrated circuit includes a variety of internal signals that remain strictly internal to the operation of the application specific integrated circuit never exposed through the supported, specified programming interface.
Problems may arise in the debug of an application specific integrated circuit and/or the testing of an application specific integrated circuit. Particular error condition may not be detectable or capable of diagnosis solely from the information provided in the standard, specified programming interface and an external processor. Rather, substantial status information available only through internal signals of the application specific integrated circuit may be required for debug and/or diagnosis of certain failures in the integrated circuit.
In the context of design debug of an integrated circuit, such internal signals may be evaluated during simulation testing of the circuit design. However, in the context of a completed, packaged, manufactured integrated circuit, there are no practical techniques presently employed to monitor the state of internal signals not exposed to an external processor. Once the integrated circuit is fabricated as a die with an appropriate package, diagnosing failures involving such internal signal information is difficult if not impossible.
It is evident from the above discussion that a need exists for an improved circuit design that permits dynamic, flexible test and diagnosis of a completed application specific integrated circuit (e.g., in its packaged form) that provides access to internal signals of the application specific integrated circuit not otherwise accessible through the standard, specified program interface of an attached processor.